The present invention relates generally to turbines and particularly to land-based gas turbines for power generation employing closed-circuit steam cooling paths for cooling the hot gas path components and returning the spent cooling steam to a return, for example, a heat recovery steam generator used in a combined cycle system. More particularly, the present invention relates to methods for disassembling, replacing and assembling parts of the steam cooling system of the gas turbine.
Steam cooling of hot gas path components, for example, the buckets of a gas turbine, has been proposed in the past and found efficacious in land-based power generating plants. While gas turbines are typically air-cooled, for example, jet engines employ compressor discharge air for cooling the hot gas components, steam cooling is more efficient in that the losses associated with the use of steam as a coolant are not as great as the losses realized by extracting compressor bleed air for cooling purposes. Also, in combined cycle operations, steam cooling is particularly advantageous because the heat energy imparted to the steam as it cools the gas turbine components is recovered as useful work in driving the steam turbine in the combined cycle operation.
In U.S. Pat. No. 5,593,274, of common assignee herewith, there is disclosed a gas turbine having coaxial steam passages for supplying cooling steam to hot gas components of the rotor, for example, the buckets, and returning the spent cooling steam to a return. Various refinements and improvements, however, in the supply and return of the steam for cooling purposes are provided by the present invention.
The present invention provides methods for disassembling the component parts of the closed-circuit steam cooling system of a gas turbine rotor, replacing one or more parts of the disassembled steam cooling system with fresh or new parts and reinstalling the parts including the new parts into the turbine for purposes of refurbishing the cooling system. Before describing these methods, an understanding of the closed-circuit steam cooling system for the gas turbine is necessary. In general, the system includes a bore tube assembly for receiving cooling steam from a cooling inlet scroll for passage of steam generally along the axis of the gas turbine rotor. The supplied cooling steam is turned in a generally radial direction for flow through tubes in an aft shaft disk for conveying the cooling steam adjacent the rim of the rotor. The cooling steam is supplied axially along the rim of the rotor by a plurality of supply passages or tubes extending through openings in the stacked wheels and spacers forming the gas turbine rotor. Each supply passage or tube supplies cooling steam to a supply manifold segment, a plurality of which segments are circumferentially spaced one from the other about the rotor. Each supply manifold segment includes a plurality of exit ports and supply passageways for supplying cooling steam to each of first and second buckets of respective turbine wheels, preferably of the first and second stages of the gas turbine for cooling the buckets. Spent cooling steam is returned from the buckets via return passageways and inlet ports to a plurality of return manifold segments circumferentially spaced one from the other about the rim of the rotor. The return manifold segments are each connected to an axial return tube extending along the rim of the rotor to the aft shaft disk. The spent cooling steam flowing axially along the return tubes is supplied to radial tubes extending in the aft disk for return to the bore tube assembly and exit to a return, for example, a heat recovery steam generator of a combined cycle system.
Various aspects of the generally afore described cooling steam system are of particular significance. For example, the flow of the supply and return thermal medium changes between radial and axial directions at the rim of the rotor. Elbows of novel configuration and use are provided in radial opening slots in the aft disk in communication with the axial and radial tubes for changing the direction of flow. For example, elbows are provided interconnecting the radial supply tubes for turning the flow of the supply steam from radial directions into an axial direction in communication with the steam supply tubes along the rim of the rotor. Likewise, elbows interconnect the axial return tubes with the radial tubes for changing the direction of flow of the spent cooling medium from an axial direction to radial directions. The elbows are preferably integrally cast parts readily assembled into the slots of the aft disk.
The cooling steam supply and spent cooling steam return manifolds are manifested in circumferentially spaced manifold segments. The supply and return manifold segments are also axially spaced from one another. Each manifold lies in communication with the buckets of a pair of adjacent wheels. For example, each supply manifold segment lies in communication with certain buckets of adjacent wheels on opposite axial sides thereof. Likewise, the return manifold segments receive spent cooling steam from certain buckets which also lie on opposite sides of the return manifold segments. Spoolies are used to interconnect the supply and return manifold segments with the various passages in the buckets.
It will be appreciated that the above-described cooling system is formed of various component parts which are susceptible to degradation by the flow of steam and that, as a result, such parts may fail over time. It is therefore desirable to refurbish the steam cooling system of the turbine, preferably at scheduled outages, by replacing parts thereof which have degraded or which should be replaced on a scheduled maintenance basis. As a consequence, it is necessary to have access to the various parts of the steam cooling system within the turbine rotor in order to replace such parts. The present invention permits the disassembly and removal of the various parts of the steam cooling system and the installation of replacement parts in lieu thereof.
To accomplish the foregoing, the supply and radial tubes of the aft disk and the supply and return axial tubes extending through the rim of the rotor may be removed by first removing the elbows on the aft disk which turn the flow between radial and axial directions. The elbows are mounted in dovetail grooves on the aft disk for removal in an axially aft direction. The elbows support the radial tubes in their outermost radial positions by spring clips interconnecting the elbows and radial tubes. By removing the spring clips and a retention ring for the elbows, the elbows are displaced in an axially aft direction which frees the radial tubes for removal in a radially outward direction from the aft disk.
When the elbows are removed, retention plates which secure the axially extending supply and return tubes against axial movement in an aft direction are displaced in a circumferential direction followed by radial movement. This frees the axial tubes for removal from the wheels and spacers of the rotor in an axially aft direction. Upon withdrawal of the axial tubes, the spoolies interconnecting the axial tubes and the manifolds are withdrawn therewith or may be withdrawn separately through the aligned openings of the wheels and spacers.
By removing the buckets of adjacent wheels, the crossover tubes between the supply and return manifolds and the buckets are exposed for axial withdrawal. After removal of the crossover tubes, the manifold segments are disconnected from the spacer by a radial inward movement followed by an axial movement and a radial outward movement.
The bore tube assembly is likewise removed from the rotor. Radially extending pins are first disconnected from the aft disk thereby releasing the end cap assembly from the aft disk. The bore tube assembly can then be axially withdrawn in an aft direction from the rotor.
It will be appreciated that with all of the various parts of the cooling system withdrawn from the rotor, the parts can be inspected and replaced as needed or on a scheduled basis. The reverse procedure is employed to reinstall the parts of the cooling system as explained in detail below.
In a preferred embodiment according to the present invention, there is provided in a turbine rotor having axially spaced wheels mounting buckets, and spacers between the wheels, and a closed circuit cooling system for cooling the buckets, comprised of a plurality of parts for flowing a cooling medium, the parts including a plurality of tubes disposed within the rotor defining flow passages for flowing the cooling medium to and from the buckets, a method of repairing one or more of the parts of the cooling system, comprising the steps of removing at least one of the tubes from the rotor and installing in the rotor the one tube repaired or a replacement part for the one tube.
In a further preferred embodiment according to the present invention, there is provided in a turbine rotor having axially spaced wheels mounting buckets, and spacers between the wheels, a cooling system for cooling the buckets, comprised of a plurality of parts for flowing a cooling medium, the parts including a plurality of generally axially extending tubes circumferentially spaced from one another about the rotor defining flow passages for flowing the cooling medium, a plurality of generally radially extending tubes defining flow passages for flowing the cooling medium, and an aft disk forming part of the rotor and having a plurality of flow turning elements interconnecting the axial and radially extending tubes, the flow turning elements having passageways for communicating and turning the cooling medium between the flow passages of the axial and radial tubes, a method of disassembling at least a portion of the cooling system, comprising the steps of removing the flow turning elements from the aft disk, removing the radial tubes from the aft disk in a radial outward direction and removing the axial tubes in a generally aft direction.
In a still further preferred embodiment according to the present invention, there is provided in a turbine rotor having axially spaced wheels mounting buckets, and spacers between the wheels, and a closed circuit cooling system for cooling the buckets, comprised of a plurality of parts for flowing a cooling medium within the rotor to and from the buckets, a method of repairing one or more of the parts of the cooling system, comprising the steps of removing at least one of the cooling system parts from the rotor and installing in the rotor the one cooling system part repaired or a replacement part for the one cooling system part.